Coated diamonds for use in impregnated diamond bits

ABSTRACT

An insert for an impreg bit that includes coated diamond particles disposed in a matrix material, wherein the coated diamond particles include a boride, a nitride, and a carbide of a group IVA, VA, VI transition metal or silicon disposed on synthetic, natural, TSP diamonds, or combinations thereof is disclosed. A method of forming a diamond-impregnated insert, including coating a plurality of diamond particles with a coating formed from a boride, a nitride, and a carbide of a group IVA, VA, VI transition metal or silicon or mixtures thereof, and forming a diamond impregnated insert body is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 60/498,543, filed Aug. 28, 2003. This provisional application is hereby incorporated by reference in its entirety.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates generally to drill bits used in the oil and gas industry and more particularly, to drill bits having diamond-impregnated cutting surfaces. Still more particularly, the present invention relates to drag bits in which the diamond particles imbedded in the cutting surface have a coating to improve diamond bonding and/or reduce diamond degradation.

2. Background Art

In the drilling industry, it is well known that different types of bits work more efficiently with different formations. Rotary drill bits with no moving elements on them, referred to as “drag” bits, may be used to drill very hard or soft formations depending on the type of drag bit. Drag bits include bits having cutting elements attached to the bit body, such as polycrystalline diamond compact insert bits, and those including abrasive material, such as diamond, impregnated into the bit body material that engages the formation. The latter bits are commonly referred to as “impreg” bits.

An example of a prior art diamond impregnated drill bit is shown in FIG. 1. The drill bit 10 includes a bit body 12 and a plurality of ribs 14 that are formed in the bit body 12. The ribs 14 are separated by channels 16 that enable drilling fluid to flow between and both clean and cool the ribs 14. The ribs 14 are typically arranged in groups 20 where a gap 18 between groups 20 is typically formed by removing or omitting at least a portion of a rib 14. The gaps 18, which may be referred to as “fluid courses,” are positioned to provide additional flow channels for drilling fluid and to provide a passage for formation cuttings to travel past the drill bit 10 toward the surface of a wellbore (not shown).

Diamond impregnated drill bits are particularly well suited for drilling very hard and abrasive formations. The presence of abrasive particles both at and below the surface of the matrix body material ensures that the bit will substantially maintain its ability to drill a hole even after the surface particles are worn down.

During abrasive drilling with a diamond-impregnated cutting structure, the diamond particles scour or abrade away the rock. As the matrix material around the diamond crystals is worn away, the diamonds at the surface eventually fall out and other diamond particles are exposed.

Impreg bits are typically made from a solid body of matrix material formed by any one of a number of powder metallurgy processes known in the art. During the powder metallurgy process, abrasive particles and a matrix powder are infiltrated with a molten binder material. Upon cooling, the bit body includes the binder material, matrix material, and the abrasive particles suspended both near and on the surface of the drill bit. The abrasive particles typically include small particles of natural or synthetic diamond. Synthetic diamond used in diamond impregnated drill bits is typically in the form of single crystals. However, thermally stable polycrystalline diamond (TSP) particles may also be used.

In a typical impreg bit forming process, the shank of the bit is supported in its proper position in the mold cavity along with any other necessary formers, e.g. those used to form holes to receive fluid nozzles. The remainder of the cavity is filled with a charge of tungsten carbide powder. Finally, a binder, and more specifically an infiltrant, typically a nickel brass copper based alloy, is placed on top of the charge of powder. The mold is then heated sufficiently to melt the infiltrant and held at an elevated temperature for a sufficient period to allow it to flow into and bind the powder matrix or matrix and segments. For example, the bit body may be held at an elevated temperature (>1800° F.) for a period on the order of 0.75 to 2.5 hours, depending on the size of the bit body, during the infiltration process.

By this process, a monolithic bit body that incorporates the desired components is formed. It has been found, however, that the life of both natural and synthetic diamond is shortened by the lifetime thermal exposure experienced in the furnace during the infiltration process. Accordingly, it is desired to provide a technique for manufacturing bits that includes imbedded diamonds that have not suffered the thermal exposure normally associated with the manufacture of such bits. Furthermore, it is desirable to provide a bit that includes diamond particles in its primary or leading cutting structures without subjecting the diamond particles to undue thermal stress or thermal exposure. Such a bit structure is disclosed in U.S. Pat. No. 6,394,202 (the '202 patent), which is assigned to the assignee of the present invention and is hereby incorporated by reference.

Referring now to FIG. 2, a drill bit 20 in accordance with the '202 patent comprises a shank 24 and a crown 26. Shank 24 is typically formed of steel and includes a threaded pin 28 for attachment to a drill string. Crown 26 has a cutting face 22 and outer side surface 30. According to one embodiment, crown 26 is formed by infiltrating a mass of tungsten-carbide powder impregnated with synthetic or natural diamond, as described above.

Crown 26 may include various surface features, such as raised ridges 27. Preferably, formers are included during the manufacturing process so that the infiltrated, diamond-impregnated crown includes a plurality of holes or sockets 29 that are sized and shaped to receive a corresponding plurality of diamond-impregnated inserts 10. Once crown 26 is formed, inserts 10 are mounted in the sockets 29 and affixed by any suitable method, such as brazing, adhesive, mechanical means such as interference fit, or the like. As shown in FIG. 2, the sockets can each be substantially perpendicular to the surface of the crown. Alternatively, and as shown in FIG. 2, holes 29 can be inclined with respect to the surface of the crown 26. In this embodiment, the sockets are inclined such that inserts 10 are oriented substantially in the direction of rotation of the bit, so as to enhance cutting.

As a result of the manufacturing technique of the '202 patent, each diamond-impregnated insert is subjected to a total thermal exposure that is significantly reduced as compared to previously known techniques for manufacturing infiltrated diamond-impregnated bits. For example, diamonds imbedded according to methods disclosed in the '202 patent have a total thermal exposure of less than 40 minutes, and more typically less than 20 minutes (and more generally about 5 minutes), above 1500° F. This limited thermal exposure is due to the shortened hot pressing period and the use of the brazing process.

The total thermal exposure of methods disclosed in the '202 patent compares very favorably with the total thermal exposure of at least about 45 minutes, and more typically about 60-120 minutes, at temperatures above 1500° F., that occurs in conventional manufacturing of furnace-infiltrated, diamond-impregnated bits. If diamond-impregnated inserts are affixed to the bit body by adhesive or by mechanical means such as interference fit, the total thermal exposure of the diamonds is even less.

Thermal degradation is only one mechanism for bit failure in drag bits. The diamonds are also subjected to a number of different forces that may cause the diamonds to be lost from the bit. Typically, diamonds are retained merely by mechanical locking in the matrix, because the diamonds cannot be wetted by the matrix material. As such, the diamonds can be forcibly dislodged from the matrix, through the action of the various forces and/or fluids flowing around the bit. One solution, therefore, to increasing bit life is to increase the amount of force required to dislodge the impregnated diamonds from the bit.

SUMMARY OF INVENTION

In one aspect, the present invention relates to an insert for a drill that includes coated diamond particles disposed in a matrix material, wherein the coated diamond particles comprise a boride, nitride, or carbide of a group IVA, VA, or VI transition metal disposed on synthetic, natural, TSP diamonds, or combinations thereof.

In one aspect, the present invention relates to a drill bit that includes a bit body, and a plurality of ribs formed in the bit body and at least in part from a matrix material infiltrated with a binder alloy, the ribs being infiltrated with a plurality of abrasive particles, at least a portion of the abrasive particles being coated diamond particles, wherein the coated diamond particles comprise a boride, nitride, or carbide of a group IVA, VA, or VI transition metal disposed on synthetic, natural, TSP diamonds, or combinations thereof.

In one aspect, the present invention relates to a method of forming a diamond-impregnated insert, including coating a plurality of diamond particles with a coating comprising a boride, nitride, or carbide of a group IVA, VA, VI transition metal, or mixtures thereof, and forming a diamond impregnated insert body.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a prior art impreg bit;

FIG. 2 is a prior art perspective view of a second type of impreg bit;

FIG. 3 shows a process for coating diamonds in accordance with an embodiment of the present invention;

FIG. 4 shows a process for forming an insert in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

In one aspect, the present invention relates to diamonds that have a specialized coating for use in diamond impregnated bits. In selected embodiments, the coating is a boride, nitride, or carbide of a group IVA, VA, or VI transition metal (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, or mixtures thereof). In particular embodiments, the coating is a silicon carbide. Other silicon coatings may be used as well. Further, those having ordinary skill in the art will recognize that other coatings may be used. The present inventors have discovered that by providing a strongly bonded wettable coating for the diamonds, enhanced diamond bonding and/or retention strength results, improving the performance of the impreg bit.

In one embodiment of the invention, coated diamonds 100 are manufactured prior to the formation of the impregnated bit, as shown for example in FIG. 3. In this embodiment, uncoated diamond particles 90 are placed on a work surface 92. The diamond particles can be natural, synthetic, or TSP diamonds, or a combination of some or all of these types.

The manufacture of TSP is known in the art, but a brief description of the process is provided herein. When formed, diamond tables comprise individual diamond “crystals” that are interconnected by diamond to diamond bonds. The bonded diamond crystals thus form a lattice structure. Metal catalysts such as cobalt are often found within the interstitial spaces in the diamond lattice structure. Cobalt has a significantly different coefficient of thermal expansion as compared to diamond, so upon heating of the diamond table, the cobalt will expand, causing cracks to form in the lattice structure, resulting in deterioration of the diamond table. In order to obviate this problem, strong acids are used to “leach” the cobalt from the diamond lattice structure.

After being placed on a work surface 92, the uncoated diamond particles 90 are treated with a coating 94. Those having ordinary skill in the art will recognize that no limitation on the scope of the present invention is intended by the description of any one process. In one embodiment, chemical vapor deposition (CVD) may be used to apply a TiC coating to diamonds. Those having ordinary skill in the art will recognize that CVD processes are known in the art, and the particular process used is not intended to limit the scope of the present invention. In CVD, the coating chemically bonds to the diamond crystals, resulting in a strong bond between the coating and the diamond crystals. In addition, the coating may be applied to synthetic, natural, and/or TSP diamonds, depending on the particular application.

Those having ordinary skill in the art will recognize that a number of other techniques may be used to apply the coating to the diamonds, and that no limitation on the scope of the present invention is intended by the above description. Moreover, while this embodiment discloses using a titanium carbide coating, it is expressly within the scope of the present invention that the coating may be a boride, nitride, or carbide of a group IVA, VA, or VI transition metal (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, or mixtures thereof). In addition, the coating may be a silicon carbide. Other silicon coatings may be used as well. Further, those having ordinary skill in the art will recognize that other coatings may be used.

Next, the coated diamond particles 100 and powdered matrix material are placed in a mold. The contents are then hot-pressed or sintered at an appropriate temperature, preferably between about 1500 and 2200° F., more preferably between about 1800° F. to about 2100° F., to form an insert or coated bit body. While embodiments of the invention may be used to manufacture an insert or an impreg bit, for clarity, the following description is focused on the formation of an insert. One of ordinary skill in the art would appreciate that the coated diamond of the invention may also be used to form bit bodies using any suitable method known in the art. Heating of the material can be by furnace or by electric induction heating, such that the heating and cooling rates are rapid and controlled in order to prevent damage to the diamonds. The inserts may be heated by resistance heating in a graphite mold. The dimensions and shapes of the inserts and of their positioning on the bit can be varied, depending on the nature of the formation to be drilled.

The matrix in which the coated diamonds are embedded to form the coated diamond impregnated inserts preferably satisfies several requirements. The matrix preferably has sufficient hardness so that the diamonds exposed at the cutting face are not pushed into the matrix material under the very high pressures encountered in drilling.

In addition, the matrix preferably has sufficient abrasion resistance so that the diamond particles are not prematurely released. Lastly, the heating and cooling time during sintering or hot-pressing, as well as the maximum temperature of the thermal cycle, preferably are sufficiently low that the diamonds embedded therein are not thermally damaged during sintering or hot-pressing.

To satisfy these requirements, as an exemplary list, the following materials may be used for the matrix in which the coated diamonds are embedded: tungsten carbide (WC), tungsten alloys such as tungsten/cobalt alloys (W—Co), and tungsten carbide or tungsten/cobalt alloys in combination with elemental tungsten (all with an appropriate binder phase to facilitate bonding of particles and diamonds), and the like. Those of ordinary skill in the art will recognize that other materials may also be used for the matrix, including titanium-based compounds, nitrides (in particular cubic boron nitride), etc.

It will further be understood that the concentration of diamond in the inserts can differ from the concentration of diamond in the bit body. It should be noted that combinations of coated and uncoated diamonds may be used, depending on the particular application. According to one embodiment, the concentrations of diamond in the inserts and in the bit body are in the range of 50 to 150 (100=4.4 carat/cc). Those having ordinary skill in the art will recognize that other concentrations of diamonds may also be used depending on particular applications.

Initial tests of bits manufactured according to the above process have indicated that bit performance is significantly enhanced by the use of the coated diamonds. The reasoning behind the improved performance is believed to result from the bonding that occurs between the matrix material and the coating. Uncoated diamonds do not significantly bond to the matrix material. Application of the coating provides a surface layer on the diamonds that is wettable and bondable to the tungsten carbide matrix and GHI bond materials. This allows the diamonds to bond to the matrix instead of just being held by mechanical locking. In addition, some of the coatings are believed to retard diamond degradation that would otherwise occur during the processing of the bit.

It will be understood that the materials commonly used for construction of bit bodies can be used in the present invention. Hence, in one embodiment, the bit body may itself be diamond-impregnated. In an alternative embodiment, the bit body comprises infiltrated tungsten carbide matrix that does not include diamond.

In an alternative embodiment, the bit body can be made of steel, according to techniques that are known in the art. Again, the final bit body includes a plurality of holes having a desired orientation, which are sized to receive and support the inserts. The inserts, which include coated diamond particles, may be affixed to the steel body by brazing, mechanical means, adhesive or the like.

One suitable method of forming an insert in accordance with the present invention is now described with reference to FIG. 4. First, a mold, which defines dimensions of an insert, is formed (400). The mold may be made of any suitable material known in the art, such as graphite. In one embodiment, the mold comprises a block having one or more holes and at least an upper and a lower plunger for each hole (not shown). Alternatively, a series of upper and lower plungers may be used. The upper and lower plunger are used to define the height of the insert. Alternatively, the hole may have a fixed bottom and only an upper plunger is required for defining the height of the insert.

After forming the mold, powder of a suitable material, as noted above, that includes the coated diamonds and the matrix powder, is loaded into the holes, with the lower plungers in place (404). Then, the upper plunger is placed into the hole, “capping” the hole shut (408). The mold assembly may then be pre-pressed in a press (410). Finally, the mold assembly is placed in the hot press furnace (412) for the production of a diamond-impregnated insert body.

Alternate methods of forming an insert may be used. For example, a high pressure, high temperature (IPHT) process for sintering diamond or cubic boron nitride may be used. Such a process has been described in U.S. Pat. Nos. 5,676,496 and No. 5,598,621 and their teachings are incorporated by reference herein. Another suitable method for hot-compacting pre-pressed diamond/metal powder mixtures is hot isostatic pressing, which is known in the art. See Peter E. Price and Steven P. Kohler, “Hot Isostatic Pressing of Metal Powders”, Metals Handbook, Vol. 7, pp. 419-443 (9th ed. 1984).

In another embodiment, the present invention relates to coated diamonds for use as abrasive particles that are impregnated into a drill bit. Typically, impreg bits are manufactured from a base matrix material that is infiltrated with binder materials. Examples of these infiltrated materials may be found in, for example, U.S. Pat. No. 4,630,692 issued to Ecer and U.S. Pat. No. 5,733,664 issued to Kelley et al. These materials are advantageous because they are highly resistant to erosive and abrasive wear, yet are tough enough to withstand shock and stresses associated harsh drilling conditions.

During the metallurgy process, coated diamonds, which comprise a coating, as described above, deposited over synthetic diamond, natural diamond, and/or TSP diamond, are added to the base matrix material, generally along the exterior surface portion of the ribs to form an impregnated drill bit. In certain embodiments, the coating comprises a boride, nitride, or carbide of a group IVA, VA, or VI transition metal, or combinations thereof. In one specific embodiment a titanium carbide coating is used. In addition the coating may be a silicon carbide. Other silicon coatings may be used as well. Further, those having ordinary skill in the art will recognize that other coatings may also be used.

In some embodiments, the coated diamond particles may be located in limited regions proximate the bit surface. In other embodiments, the coated diamond particles may be dispersed throughout the bit body proximate the bit surface. In some embodiments, the coated diamond particles may be dispersed throughout the entire bit body.

As described above, with reference to FIG. 2, impreg bits may include a plurality of gage protection elements disposed on the ribs and/or the bit body. In some embodiments of the present invention, the gage protection elements may be modified to include coated diamonds.

By positioning coated diamond particles at and/or beneath the surface of the ribs, the impreg bits exhibit increased durability and are less likely to exhibit premature wear than typical prior art impreg bits. It has been discovered that the coated diamond particles are less likely to be sheared off or “popped out” of the impreg bit than are uncoated diamond particles.

Advantageously, embodiments of the present invention provide coated diamonds that are useful in drill bit inserts or impreg bits. In particular, embodiments of the present invention improve the durability of impreg bits by increasing the amount of force required to eject diamonds from the matrix. The mechanism for this improvement is believed to result from bonding between the coating and the surrounding matrix. In addition, the coating provides additional thermal protection.

Further, embodiments of the present invention, by using a coating, reduces diamond degradation. Most of the harmful degradation occurs at the diamond surfaces, where graphitization can occur. Surface graphitization of the diamond is what hurts bonding. Internal degradation weakens diamond making it more susceptible to fracture. Generally speaking, surface graphitization is more problematic than the internal degradation. Embodiments of the present invention are particularly suited to reduce surface graphitization. No restriction on the scope of the invention is intended by the above specific examples and description.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. 

1. An insert for a impreg drill bit comprising: coated diamond particles disposed in a matrix material, wherein the coated diamond particles comprise at least one compound selected from a boride, a nitride, and a carbide of a group IVA, VA, VI transition metal or silicon disposed on synthetic, natural, TSP diamonds, or combinations thereof.
 2. The insert of claim 1, wherein the coated diamond particles are coated prior to formation of the insert.
 3. The insert of claim 1, wherein the matrix material comprises at least one material selected from tungsten carbide, tungsten alloy, tungsten carbide in combination with elemental tungsten, tungsten alloy in combination with elemental tungsten, titanium-based compounds, and nitrides.
 4. The insert of claim 1, wherein the diamonds are coated with at least one of titanium carbide and silicon carbide.
 5. An impreg drill bit comprising: a bit body; and a plurality of ribs formed in the bit body and at least in part from a matrix material infiltrated with a binder alloy, the ribs being infiltrated with a plurality of abrasive particles, at least a portion of the abrasive particles being coated diamond particles, wherein the coated diamond particles comprise at least one compound selected from a boride, a nitride, and a carbide of a group IVA, VA, VI transition metal or silicon disposed on synthetic, natural, TSP diamonds, or combinations thereof.
 6. The drill bit of claim 5, wherein the bit body comprises said coated diamond particles.
 7. An impreg drill bit, comprising: a bit body; and a plurality of inserts affixed to said bit body, at least one of said plurality of inserts comprising coated diamond particles disposed in a matrix material, wherein the coated diamond particles comprise at least one compound selected from a boride, a nitride, and a carbide of a group IVA, VA, VI transition metal or silicon disposed on synthetic, natural, TSP diamonds, or combinations thereof.
 8. The drill bit of claim 7, wherein the bit body comprises said coated diamond particles.
 9. A method of forming a diamond-impregnated insert, comprising: coating a plurality of diamond particles with a coating comprising at least one compound selected from a boride, a nitride, and a carbide of a group IVA, VA, VI transition metal or silicon; and forming a diamond impregnated insert body using the coated diamond particles and a matrix material.
 10. The method of claim 9, wherein the forming the diamond impregnated insert body uses a mold having at least one hole, and at least one upper plunger.
 11. The method of claim 10, wherein the matrix material is selected from tungsten carbide, tungsten alloy, tungsten carbide in combination with elemental tungsten, tungsten alloy in combination with elemental tungsten, titanium-based compounds, and nitrides.
 12. The method of claim 11, wherein the forming the diamond impregnated insert body is performed at a temperature of at least 1500° F. and at greatest 2200° F.
 13. The method of claim 12, wherein the forming the diamond impregnated insert body is performed at a temperature of at least 1800° F. and at greatest 2100° F.
 14. The method of claim 9, wherein the diamond impregnated insert body is formed using a high pressure, high temperature process.
 15. The method of claim 9, wherein the diamond impregnated insert body is formed using hot isostatic pressing.
 16. A method of forming a diamond-impregnated bit, comprising: coating a plurality of diamond particles with a coating comprising at least one compound selected from a boride, a nitride, and a carbide of a group IVA, VA, VI transition metal or silicon; and forming a diamond impregnated bit using the coated diamond particles and a matrix material.
 17. The method of claim 16, wherein at least one diamond-impregnated insert is affixed to a bit body.
 18. The method of claim 16, wherein the forming the diamond impregnated insert uses a mold having at least one hole, and at least one upper plunger.
 19. The method of claim 16, wherein the matrix material is selected from tungsten carbide, tungsten alloy, tungsten carbide in combination with elemental tungsten, tungsten alloy in combination with an elemental tungsten, titanium-based compounds, and nitrides.
 20. The method of claim 16, wherein the forming the diamond impregnated insert bit is performed at a temperature of at least 1500° F. and at greatest 2200° F.
 21. The method of claim 16, wherein the forming the diamond impregnated insert bit is performed at a temperature of at least 1800° F. and at greatest 2100° F.
 22. A method of drilling a formation comprising: contacting an impreg bit with the formation, wherein the impreg bit comprises a bit body; and a plurality of inserts affixed to said bit body, at least one of said plurality of inserts comprising coated diamond particles disposed in a matrix material, wherein the coated diamond particles comprise at least one selected from a boride, a nitride, and a carbide of a group IVA, VA, VI transition metal or silicon disposed on synthetic, natural, TSP diamonds, or combinations thereof. 